1. Field of the Invention
The present invention relates to a protection circuit for protecting an internal circuit from a power supply fed from outside, and an input/output circuit with the protection circuit.
2. Description of the Related Art
In recent years, smartphones have rapidly become widespread. In many smartphones, an attempt to standardize a connector has been made in order to enhance a design and reduce a circuit size. For example, a model including only a Micro-USB connector is marketed. In this model, in addition to power feeding and data communication, exchange of an audio signal is performed with one Micro-USB connector. Such connector standardization has also been attempted in other portable devices such as a portable phone, a compact PC, a digital camera, a portable music player, an IC recorder, a game machine and the like.
The Micro-USB connector includes five terminals (pins) of a power supply terminal (VBUS), a ground terminal (GND), differential paired terminals (D+, D−), and an identification line terminal (ID). Various chargers are connected to the power supply terminal, to which a voltage exceeding a set breakdown voltage may be instantaneously applied. For example, since a commercial power supply is unstable in countries or regions having poor electricity situations, a voltage exceeding the set breakdown voltage may be applied from an AC-DC adaptor. Use of an element having a high breakdown voltage against the above-described contingency will lead to an increase in circuit size.